During combustion, an internal combustion engine oxidizes gasoline and combines hydrogen (H2) and carbon (C) with air. Combustion creates chemical compounds such as carbon dioxide (CO2), water (H2O), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other compounds. A catalytic converter treats exhaust gases from the engine. An engine and catalytic converter are considered to be “cold” during an initial startup period after a long soak. During this cold start period, combustion of gasoline within the engine is incomplete. Further the catalytic converter does not operate optimally.
In an effort to optimize the functionality of the engine and catalytic converter during cold start conditions, vapor assist cold start methods and systems have been developed. The methods and systems facilitate the capturing of vapor fuels from a fuel tank and purging the vapor fuel as an additional source of fuel to the engine.
One deficiency in the conventional system is that when a fuel tank is full or the vehicle is sitting on a grade such that a fuel level vent valve (FLVV) of the vapor assist system closes, tank vapor space is substantially cut off to engine purge. The FLVV is designed to prevent fuel from being pumped into an on-board refueling vapor recovery (ORVR) canister when the vehicle is being re-fueled. The FLVV is not designed to remain open for engine purge when the fuel tank is full or the vehicle is resting on a grade.